In prior art electro-acoustical transducers, two separate chambers, often termed front and back volumes, exist into one of which sound from the surroundings is conveyed—or from which sound generated therein is transmitted to the surroundings. Static pressure compensation has traditionally been provided to the other chamber by a small vent or aperture between the front volume and the back volume. This vent provides a gas flow channel between interiors of the front and back volume so as to maintain a static pressure difference of substantially zero between two sides of a deflectable diaphragm. This vent or gas flow channel may have dimensions sufficiently small to prevent pressure changes with frequencies much higher than a DC level to pass between the front and back volumes. Consequently, the vent may only serve the purpose of pressure equalization in the inner space, or back volume, not connected directly with the surroundings via the sound port. A transducer of this type is disclosed in U.S. Pat. No. 4,450,930.
In applications where the sound port of the transducer is blocked by the air impervious member it has been found advantageous to provide pressure equalization of both inner spaces independently of the sound port.